1. Field of the Invention
The present invention relates generally to the conversion of hydrocarbons and more particularly to converting heavy hydrocarbons laden with impurities into light hydrocarbons that can be separated into cuts of conventional products.
2. Description of Related Art
It is widely known that all refining processes leave heavy residues that are poorly fusible or solid, which find few users and few outlets. It is also widely known that oil wells often encounter deposits containing crudes that are characterized by a very high density and a very high viscosity, thus difficult to transport as such. These crudes are also characterized by a strong metal content such as Nickel and Vanadium, sediments and sludge, sulfur, salt, to mention only the main impurities, which constitute poisons for any type of catalyst. Furthermore, regardless of what is done, it is impossible to completely avoid the deposits of these components on everything that comes into contact with these crudes. Thus it is understood that if any catalyst is used, all of its surface and all its pores will be quickly covered and the catalyst will be totally dead: then it would only occupy space in the reactor, even risking plugging it if grains are accumulated in the catalyst by the cement constituted by the sediments, nickel, vanadium, asphalts, carbon produced, etc.
We know processes such as the FCC, which attempt to adjust to carbon deposits by burning them in a regenerator, but this requires a complex circulation of the catalyst between the reactor and the regenerator. Furthermore, the circulation of said catalyst creates delicate problems of erosion, through both the actual wear of the matter itself, which is sometimes perforated, and that of the catalyst which, once worn, produces dangerous dusts for any human being that no filter, no matter how large and advanced, will be able to stop. Following all the constraints encountered and compromises to be made, this type of unit can only treat distillates under vacuum (DsV), that is by eliminating from the feed the residues under vacuum (RsV) in which the metals, sediments, etc. are concentrated. Furthermore, the regenerator that burns the coke formed imposes a minimum temperature of the order of 700° C. so that the combustion may occur. The catalyst exiting the regenerator, sent into the reactor at this excessive temperature, leads to an abundant production of gaseous products, as well as highly aromatic heavy products that lost a significant quantity of hydrogen during the first contact with the catalyst that was too hot. Furthermore, it is impossible to change the spectrum of distribution of liquid conversion products which, moreover, are accompanied by a significant quantity of gas C1 C2 and LPG C3, C4.
The FCC only rearranges the distribution of the carbon and hydrogen in the molecules: it samples hydrogen in the high molecular weight molecules (high boiling temperature) to create light molecules, but the C4, C3, C2 and, in particular, C1 (CH4) take a large portion of the hydrogen. There is even a discharge of pure hydrogen. As a result, the heavy cuts knows as HCO are poor in hydrogen and cannot be recycled for a new conversion. Therefore, the conservation during the conversion of a good Hydrogen/Carbon ratio is vital.
The purpose of hydrocracking is precisely to increase the H/C ratio by adding hydrogen to the feed in an efficient manner. This process that consumes hydrogen requires the use of a hydrogen production unit which uses a lot of power and gaseous hydrocarbon containing matter (generally with a discharge of CO2 if CnH (2n+2)) is used as the starting point. Furthermore, the hydrogen becomes reactive only at pressures greater than 100 bars; this imposes a construction with very high thicknesses. The conjunction of the presence of hydrogen at temperatures of the order of 450° C. under 150 bars, in order to illustrate the ideas, presents delicate problems of realization and technology, in particular regarding the nature of the special alloy steels that are appropriate for these applications. Moreover, the conversion products saturated with hydrogen are highly paraffinic and, therefore, give gasolines with a poor octane number. Therefore, it is necessary to use a catalytic reformer that removes hydrogen in order to increase the octane number. It seems paradoxical in these operations to begin by adding hydrogen to the products with great difficulty to then being forced to remove the same. Thus it is easy to understand why it is important to avoid useless operations in all of these operations regarding the hydrogen content.
Some research efforts were carried out attempting to create active hydrogen, designated as H., in order to incorporate the same into hydrogen-poor feeds. The creation of said H. requires a great deal of energy that is returned at the time of the final reaction and “blows up” the hydrocarbon molecules in question, possibly releasing the carbon. As a consequence, instead of incorporating hydrogen into the feed, unsaturated gases are created (generally 20 to 40% of the feed) by rejecting hydrogen overall.
Other research work was carried out regarding the use of hydrogen superheated at 1100-1200° C. at 40 bars, with soaking times of 60 seconds to hydropyrolize residues of oil and heavy oils, such as those of B. SCHÜTZE and H. HOFMAN reported in Erdöl und Kohle-Erdgas-Petrochemie vereinigt mit Brennstoff-Chemie 1983, 36 No. 10,457-461. The results obtained always comprise high gas proportions (12 to 27%) and a large quantity of coke. From a thermodynamic standpoint, these two approaches are inefficient, as confirmed by all the practical results obtained (excess production of gas and coke).
It is widely known that the molecules composing the residue under vacuum may be “shaken” thermally with a VISCOSITY BREAKER (or Visbreaker), in order to “break” the viscosity. This creates a small additional production of feed that is generally converted with the FCC. We then have a visbreaker residue that is generally referred to as flash visbreaker residue (RVR), which can only be used as a heavy industrial fuel if light products such as gas oil or LCO (FCC gas oil) are added thereto in order to achieve a normal viscosity.
These examples illustrate the complexity of the refining operations with imbricated treatments and retreatments. The physical state of the matter (liquid, solid or gas) must receive a great deal of attention under normal conditions of temperature close to 20° C., and pressure close to 1 atmosphere.
We also know the COKERS that treat the residue to release the liquids while rejecting solid carbon, which will have the same applications as coal (also with the same difficulties).
We also know the improvement attempts carried out with the FLEXICOKER, which actually consists in gasifying the coke produced. The gasification requires a facility as large as that required by coking. It saturates the refinery with a fatal combustible gas that must be exported or used for other purposes than those that are strictly required for refining operations (i.e. to produce electrical power).
We also know the attempt to hydroconvert the RsV, known as the HYCON PROCESS, which would consume approximately 2.3% hydrogen. The 41% converted must be run through the FCC, with all the consequences that were mentioned in relation thereto, in particular regarding the direct leak of H2 and the loss of hydrogen contained in gases such as CH4 and C2H6.
These two processes are too complex and ultimately too difficult to implement in an efficient refining layout.
FW and UOP indicated on Oct. 27, 1997, that they implemented a catalytic process called AQUACONVERSION PROCESS in collaboration with UNION CARBIDE, for the catalyst. In practice, the general problems that are specific to catalysts remain intact. ELF ANTAR also claimed the preparation of an Aquazole containing 10 and 20% water, stable only from 15 days to one month.